LITTER AS A REGULATOR OF N AND C DYNAMICS IN MACROPHYTIC PATCHES IN NEGEV DESERT SOILS

In desert ecosystems, nutrient cycling activity is concentrated in bri ef periods of intense biological activity following wetting events. Re lease and uptake of N from litter and microbial biomass may be importa nt regulators of N availability to plants and N loss to denitrificatio n and NH3 volatilization. Litter and microbial biomass dynamics may al so be important to the maintenance of shrub-dominated patches of high fertility in desert ecosystems. We have measured soil C and N cycling processes (respiration, NH4+ and NO3- dynamics, denitrification and mi crobial biomass C and N dynamics) in rewetted Negev desert soil treate d with different size classes of desert plant litter in 30-day laborat ory incubations. The results suggest that litter plays a strong role i n conserving N following wetting events in Negev soils. Amounts of soi l NH4+ and NO3- and microbial biomass N were reduced in litter-amended treatments, suggesting that significant quantities of N were sequeste red in litter, especially the largest size classes of litter. Denitrif ication was a significant sink for N, and was stimulated by the presen ce of litter, but was less important than immobilization of N in litte r. Immobilization and release of N by litter may be especially importa nt in the N cycle in desert ecosystems, moderating seasonal patterns o f N availability and regulating patch interactions that facilitate the development of ''islands of fertility'' in these ecosystems.